The present invention relates to a process to combat harmful organisms originating in seeds or soil by means of seed treatment. The process according to the present invention is intended for the treatment of agricultural, horticultural or forestry seeds, in particular for grain.
It is known that harmful organisms which are seed-transferrable, i.e. adhere to the surface of a seed, and/or are within a seed and which damage the germinating seed and the young plants in the soil are combated with the aid of chemical and physical seed-treatment methods prior to sowing. In particular, prior to their use the grain seeds are subjected to a dressing procedure by which the spreading of such harmful organisms is to be prevented or restricted.
A chemical seed treatment using chemical dressing agents has however many disadvantages, such as toxicity for warm-blooded animals, resistance phenomena that can be observed with harmful organisms after an extensive use of dressing agents, phytotoxic effects on the cultivated plant, insufficient adhesion of the dressing agent to the seeds and negative effects on man and environment by biologically highly efficient chemical substances.
As for physicial methods in which the seeds are heated up to a temperature critical to microbial harmful organisms by means of light of different wavelengths, microwaves, water vapour, hot air, etc., only hot water dressing has temporarily gained some importance. However, such dressing agents are relatively difficult to handle. The use of high energy rays ( .gamma. rays, X-rays) to combat microbial harmful organisms is not possible on seeds because the necessary radiation dose for achieving a fungicidal effect on the seeds is phytotoxic or mutagenic.
It is already known in the prior art that seeds are subjected to an irradiation with low energy electrons in vacuum or in a free atmosphere to combat harmful organisms (DD-PS 242 337, DD-PS 238 715, U.S. Pat. No. 4,633, 611). Electron energy and radiation dose are chosen such that microbial harmful organisms are killed without any produce-affecting or phytotoxic effects on the germ of the seed corns. This method has the advantage that the seeds treated in this way will not be a hazard to people during sowing and will not pollute the environment with toxic substances. However, irradiation with low energy electrons has turned out to be unsatisfactory because seed-transferrable harmful organisms are not or only partly combated in the deep layers of the seed corn and in the seed germ and because the seeds are exposed to the attack of soil-borne harmful organisms in an unchecked and unprotected way after sowing.
Biological combating methods which employ microbial antagonists to combat fungal harmful organisms are nowadays suggested more and more often (cf., e.g., DD-PS 250 456, EP-A-304178, U.S. Pat. No. 4 798 723, etc.). In this respect the use of microbial antagonists against various seed-borne and soil-borne fungal organisms with a harmful effect is suggested. Bacterial antagonists, such as Bacillus spp., Streptomyces spp., Pseudomonas spp., Penicillium spp., Trichoderma spp. are inter alia used. However, the good fungicidal effects of these antagonists found under laboratory conditions at optimum temperatures of more than 20.degree. C. have not always been confirmed by outdoor tests, and there is considerable uncertainty about the effects thereof.
As far as an efficiency improvement is concerned, one knows that microbial antagonists are mixed with fungicides and that these mixtures are used for seed treatment (cf., e.g., DE-OS 23 52 403, DE-OS 27 40 052, DD-PS 26 74 420).